Some displays, such as liquid crystal displays (LCDs), comprise a spatial light modulator that is illuminated by a backlight. Light from the backlight interacts with the spatial light modulator which spatially modulates the light so as to present images to a viewer. The images may be still images or video images for example. The spatial light modulator may comprise an array of controllable pixels.
In some such displays, the backlight includes multiple light emitting devices, such as LEDs, for illuminating regions of the spatial light modulator. Such light emitting devices or groups of such light emitting devices may be separately controllable so that the intensity of light emitted by the backlight can be made to vary in a desired way over the spatial light modulator. Such displays are referred to herein as dual-modulation displays. Some examples of dual modulation displays are described in: U.S. Pat. No. 7,403,332 issued 22 Jul. 2008 and entitled “High Dynamic Range Display Devices”, and United States Patent Application Publication No. 2008/0180466 published 31 Jul. 2008 and entitled “Rapid Image Rendering on Dual-Modulator Displays”, which are hereby incorporated herein by reference for all purposes.
A challenge associated with dual-modulation displays is to provide a backlight capable of providing illumination having an intensity and/or spectral composition that varies in a desired way from point to point on the spatial light modulator.